A comparison of Listeria monocytogenes serovar 4b isolates of clinical and food origin in Japan by pulsed-field gel electrophoresis

Abstract

Pulsed-field gel electrophoresis (PFGE) patterns of 102 L. monocytogenes serovar 4b isolates from patients and foods examined in Japan were compared with 16 isolates from foodborne listeriosis episodes which occurred in North America or Europe. Using a combination of PFGE patterns with the restriction enzymes SmaI, ApaI, AscI and Sse8387I, 82 clinical isolates from Japan were categorized into 45 PFGE types: the largest group of 17 isolates (20.7%) were of the same PFGE type as cultures from the large foodborne outbreaks which occurred in California (1985) and Switzerland (1983–1987). Twenty cultures from foods on retail sale in Japan were classified into 12 PFGE types: four isolates were of three PFGE types also recognized among isolates of clinical origin from Japan, including the predominant clinical type.

Introduction

Outbreaks of foodborne listeriosis were first recognized during the 1980s (Schlech et al., 1983, Fleming et al., 1985, McLauchlin et al., 1991, Jacquet et al., 1995), and it is now known that the consumption of contaminated food is the primary vehicle of transmission (Rocourt and Cossart, 1997, McLauchlin, 1997). Human listeriosis was first recognized in Japan in 1958 (Ito et al., 1959), and although 20–60 sporadic cases are reported every year, specific food vehicles of infection have not been identified.

L. monocytogenes serovar 4b accounts for 60% of the reported human listeriosis in Japan, and strains of serovar 1/2b are responsible for about 30% (Terao, 1991); The predominance of serovar 4b strains is similar to that observed in other countries (McLauchlin, 1990, Farber and Peterkin, 1991). Surveys of food in Japan have shown that among the L. monocytogenes recovered from ready-to-eat foods and raw meat, 25 and 15%, respectively, were serovar 4b (Kokubo et al., 1992; Nakama, unpublished observation). In this study, molecular typing using pulsed-field gel electrophoresis (PFGE) was used to compare L. monocytogenes serovar 4b isolates from listeriosis patients and foods of Japanese origin together with isolates from foodborne incidents which have occurred in North America and Europe.